1. Field of the Invention
The present invention relates to an image sensing apparatus and an image sensing method, and more particularly, to an image sensing apparatus and an image sensing method capable of detecting a subject from a sensed image.
2. Description of the Related Art
Conventionally, in a digital camera, there is an image sensing apparatus equipped with an automatic exposure control function that determines exposure automatically based on image data obtained by image sensing. As photometric methods carried out for the purpose of such automatic exposure control, there is, for example, evaluative photometry carried out taking the entire frame into consideration, as well as multi-division photometry, in which a photometric area within the frame is divided into a plurality of blocks and photometry carried out in blocks. In addition to these methods, there is also center-weighted photometry, in which photometry is carried out with emphasis on the center portion of the frame, as well as spot photometry, in which photometry is carried out only for an arbitrary range of the center portion of the frame.
In addition, in order to get the luminance proper for a main subject, there are apparatuses in which the user specifies the area in which the main subject is present and the apparatus adjusts the exposure on the basis of the luminance of the specified area. Further, a camera that automatically detects, for example, a face as the main subject by a technique such as shape analysis from image data obtained by image sensing and carries out exposure control so that the detected face is properly exposed has been proposed (see, for example, JP-2003-107555-A). Such a camera brightens the entire frame if the face is underexposed and darkens the frame overall if the face is overexposed, even though the luminance of the frame overall is proper (see FIG. 7 of JP-2003-107555-A). Moreover, a camera has also been proposed that detects the face from an image obtained with a test flash and carries out exposure control so that the face area is correctly exposed even during flash image sensing (see, for example, JP-2004-184508-A).
However, with the methods disclosed in JP-2003-107555-A and JP-2004-184508-A, there are cases where it is not possible to control the flash illumination amount so that the luminance of the face is proper when conducting flash image sensing.
FIG. 9 shows an example in which it was not possible to control the flash illumination amount so that the luminance of the face is proper when conducting flash image sensing using a conventional two-stage shutter button.
Reference numeral 901 shown in FIG. 9 shows an instance in which, in an image obtained during pre-flash to determine the flash illumination amount, the face is overexposed and could not be detected. First, when the shutter button is depressed halfway (switch SW1 ON), a single image IM1P is sensed for exposure and focus control and the face is detected from the sensed image IM1P. If it is found that the face detected here is dark and the brightness needs to be adjusted with the flash, then when the shutter button is fully depressed (switch SW2 ON) a pre-flash is carried out prior to the main flash and a second image IM2P is sensed. In the second image IM2P, since the face is overexposed it cannot be detected. Consequently, the flash illumination amount that would give the face the correct luminance cannot be calculated, and as a result, the face in a third image IM3P obtained when the flash is fired in a main flash is too dark.
Reference numeral 902 shown in FIG. 9 shows an instance in which face detection is carried out in an image obtained when SW1 is turned ON and the face area is fixed at the detected area. First, a single image IM4P is sensed when switch SW1 is turned ON, the face is detected from the image IM4P, and the area of the detected face is fixed as the area used for all further control, including exposure control. If it is found that the face detected here is dark and the brightness needs to be adjusted using the flash, then when switch SW2 is turned ON a pre-flash is carried out prior to the main flash and an image IM5P is sensed. Assume here that after image IM4P is sensed but before image IM5P is sensed the image sensing angle changes and the face is no longer at the fixed face area. In that case, if the flash illumination amount is set based on the image signal from that fixed face area, then the face in an image IM6P obtained when the flash is fired in a main flash becomes too bright. The same problem arises whenever the subject moves.